1. Field of the Invention
The present invention relates to the production of solid fuel propellant oxidizers and, in particular, to an improved process for synthesizing 1,5-Dinosyl-3,3,7,7-tetrakis (difluoramino)-octahydro-1,5-diazocine (DNTDFD), which is a critical intermediate compound used in the production of 3,3,7,7-tetrakis (difluoramino) octahydro-1,5-dinitro-1,5-diazocine (HNFX), an efficient explosive and solid fuel propellant oxidizer.
2. Description of the Background
The compound HNFX is a valuable component in rocket propellant formulations because of its high explosive and oxidizing properties. HNFX is synthesized from commercially available materials using a multiple step process. The initial phase of some known processes leads to the intermediate compound DNTDFD, a critical intermediate for certain effective methods of producing HNFX. DNTDFD is processed into HNFX by one of a variety of methods, some of which are detailed in “Nitrolysis of a Highly Deactivated Amide by Protonitronium. See, Synthesis and Structure of HNFX, Robert D. Chapman, Journal of Organic Chemistry (1999, 64, 960–965).
The known methods for producing DNTDFD are described in Difluoramination of Heterocyclic Ketones: Control of Microbasicity, Robert D. Chapman, Journal of Organic Chemistry (1998, 63, 1566). The compound HNFX is similar to another explosive and propellant oxidizer, TNFX. The process of preparing TNFX is detailed in U.S. Patent Application No. 2000/0161248, to Chapman and in U.S. Pat. No. 6,417,355, also to Chapman. The precursor to TNFX is a compound very similar to DNTDFD. Both compounds are synthesized by a lengthy process requiring fluctuating temperature conditions. In preparing the precursor to TNFX, the reaction proceeds slowly and must be encouraged by cycling the temperature between −15 degrees C. and 0 degrees C. throughout the process, which reaches completion in two weeks time.
The process of preparing DNTDFD, as described in Difluoramination of Hetrerocyclic Ketones: Control of Microbasicity, Robert D. Chapman, Journal of Organic Chemistry (1998, 63, 1566 at 1570), requires a solution of fuming sulfuric acid, to which CH2Cl2 is added and cooled to −15 degrees C. Gaseous HNF2 is absorbed into the layer of CH2Cl2. The temperature is raised, briefly, so that the HNF2, may be absorbed and the mixture is recooled. Tetrahydro-1,5-bis(4-nitrobenzenesulfonyl)-1,5-diazocine-3,7-(2H, 6H) dione is added to the mixture, which is stirred for 15 days. The solution is basified and precipitated. The product, DNTDFD, is obtained. During the course of the reaction, temperature is allowed to rise gradually from −15 degrees C. to −8 degrees C. An alternate method is described, which involves the absorption of HNF2 gas into a layer of FREON® 11 trichlorofluoromethane and the addition of tetrahydro-1,5-bis(4-nitrobenzenesulfonyl)-1,5-diazocine-3,7-(2H, 6H) dione. This method involves cycling the temperature between −15 degrees C. and 0 degrees C. and requires 11 days.
Typically, FREON® 11 solvent is used as a diluent and absorbent for the difluoramine reagent. The process produces a yield of 52% of (crude) DNTDFD.
The DNTDFD is then processed into HNFX by one of the methods referenced above. There is a need for a more efficient process, which can more quickly and economically produce the intermediate compound, DNTDFD.